Hi Malcolm,
Certainly, I would wish to restore the keel so it drops as intended as the boat will be less efficient when going to windward without the keel down, as I learnt on the several occasions I forgot to drop the keel when I first owned my SeaHawk.
However, it would be an exaggeration to say you couldn't use it as a yacht. After all, the Pedro, Señorita and Ace of Sails, all use the same hull but don't include the drop keel and these are all sold as 18" draft boats. The ballast fitted in the base of the hull of the SeaHawk is very different to a Sailfish where all the weight is in the metal core of its keel. Failure to drop the keel in one of those will frequently lead to a capsize, I'm told.
The folk at Boatshed have been kind enough to send me larger unbranded versions of the images they took that appear on their site with permission to use them here. Studying them I have come to the conclusion that this is one of the rare boats supplied part-built and finished by the original owner.
I guess this is a boat you examined before purchasing yours. Perhaps you can confirm my conclusions...
Neither the pulpit nor the cockpit guard rails are of the standard types. Instead of a conventional tabernacle, the mast is stepped on a raised steel platform, necessitating longer shroud lanyards than normal and an extending strop to the forestay.

After enhancing one of the photos supplied, I believe that rather than either of the two normal mast bracing systems, this example appears to have floor to ceiling bulkheads that avoid the need for the usual A-frame arrangement of a two-berth boat. This produces a fore cabin that has been fitted with a platform similar to the four-berth model's moulding. It means it's not capable of sleeping four adults both because the bulkheads restrict fore-berth length and because the cockpit lockers are positioned for a two berth boat.
It's an interesting boat, that will suit someone, but probably not those keen to get a "standard" SeaHawk - if there is such a thing. Whereas most car owners these days change nothing, boat owners seem to delight in customising their craft.